It's actually quite easy once you know what's causing the problem. There are two different versions of libavcodec in your system. In my case I installed a fresh ffmpeg from SVN, now I first had to remove the package "libavcodec51". Then everything worked just fine.

sudo apt-get remove libavcodec51

If you still have problems there might be stale libraries in here: /usr/lib/libavcodec.*. Try moving them somewhere else and see if that helps. Otherwise, send me a comment. ;)

Tuxradar has put up a nice list of useful CLI commands and other tipps. For tip #36 to work in KDE 4, you need to type e.g. =4*5+4. I also recommend tip #49, locate will help you find the file, for me it was /etc/openoffice/sofficerc.

For kernels earlier than 2.6.29 tasks with SCHED_IDLEPRIO creating children such as boinc can freeze the entire system. The bug seems to be in the Linux scheduler: a process with idle priority can block the entire system (with *really* bad latency). It seems to me that if you use ionice, that will make it almost impossible for other tasks to do io (e.g. access the hard drive).

The workaround for boinc is not to use schedtool's SCHED_IDLEPRIO:Edit /etc/default/boinc-client and set to SCHEDULE="0". E.g.

echo SCHEDULE="0"|sudo tee /etc/default/boinc-client

You can also deinstall schedtool and ionice for now, though that won't fix the security issue. Affected Systems include Ubuntu Server 8.04 with all updates. But many other systems are likely affected if the fix has not yet been backported (fixed in 2.6.29).

Amazon's MP3 Service does it right and brings support not only for Windows and Mac OS X, but also for all major Linux distributions including Debian, Ubuntu and Fedora and SUSE. You can try it now and download This Much is True by Amy MacDonals for free. It worked flawlessly for me. The Amazon downloader is about 1 MB and needed roughly 6 MB dependencies on my system. It's not open soured thought and I think it's only available for i386.